evaluate: change shift byte-order to host-endian.

evaluate: change shift byte-order to host-endian.

The byte-order of the righthand operands of the right-shifts generated
for payload and exthdr expressions is big-endian.  However, all right
operands should be host-endian.  Since evaluation of the shift binop
will insert a byte-order conversion to enforce this, change the
endianness in order to avoid the extra operation.

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>